9 days late - light pink discharge

I'm nine days late, and I'm never late, always extremely regular. Today I noticed after I went to the bathroom and wiped, sorry TMI, there is very light pink discharge on the toilet paper, like almost not noticeable. I don't think I've ever had this before, and I feel like it's definitely too late to be possible implantation bleeding. I took a pregnancy test yesterday and it was negative. Guys, I'm never late! Could I be pregnant despite a negative hpt yesterday? Has anyone else experienced this and still been pregnant?